Reinforced concrete structure, rebar end anchor therefor and method of manufacturing

ABSTRACT

A method of forming anchors at the ends of rebars includes providing an anchor plate, forming an opening through the anchor plate that is larger than the diameter of the rebar, heating the end of a rebar, inserting it into the anchor plate opening and then forging it to upsize the rebar end into engagement with the wall of the anchor plate opening. Preferably, the wall of the opening through the anchor plate is irregular to enhance the interlock between the upsized rebar end and the anchor plate. The resulting rebar end anchor then finds particular utility in reinforced concrete structure at joint intersections of for example, a beam and column or wall.

FIELD OF THE INVENTION Background of the Invention

Concrete is characterized by high compressive strength and notoriouslypoor tensile strength. In a typical reinforced concrete structure thisdeficiency in the tensile strength of the concrete is obviated byimbedding in the concrete at those points where tensile stress will beencountered, reinforcing bars, typically of steel. Where a section of areinforced concrete structure terminates at another section, such as ata beam/wall or beam/column intersection, provision must also be made toinsure that the ends of the rebars will not pull out of the wall orcolumn when tensile stress is encountered. Conventionally, this wasremedied by bending the end of the rebar and perhaps inserting anotherrebar beneath the bend perpendicularly to the length of the first rebar.Typically, a joint of this type is congested to begin with and thisremedy compounded the congestion, resulting in higher concrete placementcosts and possible concrete consolidation problems.

To avoid these problems it is known to provide an enlarged head at therebar end, either through forging or by welding a plate on the rebarend, or providing a plate with a threaded opening, upsetting the end ofthe rebar to enlarge its diameter and then threading the enlarged endcomplementarily to the anchor plate threaded opening and screwing theplate onto the threaded rebar end.

Where the rebar ends are provided with a forged head, a very largeforging press is required, a substantial portion of the rebar must bepreheated for forging with a commensurate expenditure of time andenergy, and multiple strikes of the press are required to create theheaded end. Where the end plate is a separate part with a threadedopening receiving a threaded end of the rebar, the rebar end must firstbe upsized through a forging process before the threads are cut into therebar end. This is necessary to achieve the ultimate strength of therebar. If the rebar were threaded without upsizing the end, the threadwould create a weak point that would reduce the overall tensile strengthof the rebar.

As noted above, it is also known to weld an anchor plate to the end of arebar, typically through an inertia welding process. This approach hasthe drawbacks of requiring a separate fabricated anchor plate andrequiring the upsizing of the rebar end prior to welding, but moreimportantly, the welding process is subject to various process variablesthat contribute to quality considerations.

It will be seen, therefore, that a need exists for a rebar anchorage toreduce congestion at a joint intersection in a reinforced concretestructure, but without the disadvantages noted above with respect toconventional methods of providing an end anchorage for concretereinforcing bars.

SUMMARY OF THE INVENTION

The present invention provides a method of manufacturing an end anchorof superior structural performance but with the expenditure of lessenergy required than in comparable prior art methods, resulting in costsavings and a unique end anchor product.

Specifically, in accordance with the present invention a separate anchorplate is provided, which may be round, square, rectangular or otherconfiguration and through the plate an opening having irregular wallportions is formed. Conventional rebar having an effective outerdiameter smaller than the size of the opening through the anchor plateis preheated at its end, the heated end inserted into the openingthrough the plate and then forged onto the plate by upsizing the rebarend and filling the hole through the plate with rebar material to form amechanical interlock with the irregular wall portions of the openingthrough the anchor plate.

This method permits the use of smaller forging presses than would berequired to forge the end of a rebar into an end anchor and requiresless heat prior to forging and less strikes of the forging press tocomplete the assembly. Thus, an end anchor in accordance with thepresent invention may be produced in less time and with less energy thancomparable processes for forming rebar end anchors.

As a result, the construction of an intersecting joint, such as thetermination of a beam into a column or wall in a reinforced concretestructure is greatly facilitated, while conserving the energy andcommensurate expense thereof usually associated with end anchors of thistype. Therefore, in a typical intersection of this type, wherereinforcing bars and associated ties create a congested condition, thenecessity of contributing to that congestion by bending the end of theterminating rebar and providing cross rebar members within the bend isavoided but again, without the expense attended to conventional endanchors.

Additionally, the process of forging the rebar into the anchor plateprovides the added benefit of upsizing the rebar at the connection. Thisprovides a stronger section of rebar at the connection and ensures thatthe rebar, if subjected to ultimate tensile stress, will break at alocation distant from the anchor plate connection. This is an importantfeature because there are standards that require failure to occur awayfrom the connection. This makes it obvious that the rebar has failed andnot the anchor plate-rebar connection.

These and other objects and advantages of the present invention willbecome apparent from the following description, the accompanyingdrawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a perspective view showing a typical beam-column connectionutilizing one embodiment of end anchors in accordance with the presentinvention;

FIG. 2 is a perspective view of an end anchor plate in accordance withthe present invention illustrating an opening through the plate havingone form of irregularly shaped walls, in this embodiment, taking theform of internal grooves;

FIG. 3 is an elevational view, partly in section, showing an end of aconventional rebar about to be received in an opening through the anchorplate of FIG. 2;

FIG. 4 is a view similar to FIG. 3, but illustrating the rebar end afterit has been preheated and forged into mechanical interlock with theirregularly shaped walls of the opening through the anchor plate of FIG.3;

FIG. 5 is a view similar to FIG. 3, but showing a second embodiment ofthe invention, wherein the irregularly shaped wall portions of theopening through the anchor plate are formed as a counterbore;

FIG. 6 illustrates the end of a rebar received in the opening of theanchor plate shown in FIG. 5 after the rebar has been preheated andforged into interlocking engagement with the irregular walls of theanchor plate;

FIG. 7 is an end view of the anchor plate and forged in place rebar ofFIG. 4;

FIG. 8 is a view similar to FIG. 7 but illustrating another embodimentof the present invention, wherein the anchor plate is formed with asquare configuration;

FIG. 9 is a view similar to FIG. 8, but wherein the anchor plate isrectangular; and

FIG. 10 is a perspective view of another embodiment of anchor plateshowing another form of irregularity in the side walls of the openingthrough the anchor plate designed to be mechanically interlocked withthe heated, forged end of a rebar.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawings depicts a beam-column connection 10, whichcomprises a column 12, a through beam, consisting of beam segments 14and 16 and a beam 18 terminating at the connection. As will be apparentfrom in FIG. 1, the intersecting vertical reinforcing bars, as at 20 andthe horizontal intersecting bars, as at 22 and their associated ties, asat 24, create a congestion which, in conventional connections of thistype is exacerbated by the addition of the rebars projecting from theterminating beam, particularly where the rebars of the terminating beamare bent at substantially right angles and additional rebar inserted inthe bend to resist withdrawal. A disadvantage of this increasedcongestion is poor concrete consolidation, higher concrete placementcosts and poor in place concrete quality. This condition is amelioratedin accordance with the present invention by providing rebar 26 withanchor ends comprising anchor plates, one embodiment of which is shownat 30 and which are attached to the rebar in a method in accordance withthe present invention. While the plates 30 shown in FIG. 1 arerectangular, it will be apparent as the description proceeds that theplates may assume other configurations, such as circular and square.

Thus, as seen in FIG. 2 of the drawings, an anchor plate 32 of round orcircular configuration is shown having an opening 34 formed therethrough. As will be apparent from FIG. 2, the wall portions of theopening 34 are irregular, that is, the wall portion of the opening 34 isnot merely a smooth constant diameter surface extending through theanchor plate 32. Instead, the wall portions of the opening 34 are, inthe embodiment of FIG. 2, provided with circular grooves 36. While thegrooves 36 of FIG. 2 comprise a threaded opening, as may also be seen inFIGS. 3 and 4, it will be apparent the grooves 36 may also be simply aseries of parallel circular grooves.

In any case, it will be noted from FIG. 3 of the drawings that the outersurface of rebar 37 is provided with deformations 38 which enhance itsembedment in the concrete beam 18. While the rebars 20, 22 and 26 areshown as smooth surfaced in FIG. 1 of the drawings, in actuality all ofthe bars would preferably be provided with deformations such as at 38 asshown in FIG. 3 of the drawings. It will also be noted from FIG. 3 thatthe nominal outer diameter of the rebar 37 is smaller than the opening34 through the plate 32. This permits the anchor end 40 of the rebar tobe inserted freely into the opening 34.

However, prior to placing the anchor end 40 of the rebar 37 into theopening 34, end 40 is first heated and then, after it is received in theopening, subjected to an axial force and thus forged into place inmechanical interlocking relationship with the irregular wall portions 36of the anchor plate 32. In other words, the heated end 40 of the rebar37 is upsized by forging, filling in the irregularities 36 in theopening 34 through the anchor plate 32 with material from the rebar toform a mechanical joint. As noted above, upsizing the rebar ensures thatshould it encounter ultimate tensile stress, it will break at a pointremote from the joint with the anchor plate,

While the end anchor construction shown in FIG. 4 of the drawings isformed by forging the heated, anchor end 40 of the rebar 26 into thegrooves 36, it is possible to utilize other wall irregularities asdepicted in FIG. 5 of the drawings. Here, anchor plate 42 is providedwith a counterbored opening 44 having a first portion 46 a secondportion 48 and an interconnecting portion 50. Otherwise, the process ofmanufacturing the rebar anchor end of FIG. 5 proceeds similarly to thatprevious described. Thus, anchor end 52 of rebar 54 is first heated andthen, because the nominal diameter of the rebar 54 is smaller than thefirst portion 46 of the opening 44 through the plate 42, it is freelyreceived in the opening 44, after which the heated anchor end 52 isforged to expand outwardly and fill the entire area of the counterboreopening 44, including, not only the smaller diameter portion 46, butalso the counterbored portion 48 and the interconnecting portion 50.Thus, again the heated anchor end of the rebar is upsized to fill theopening 44 and form a mechanical joint between the rebar and the anchorplate 42.

FIG. 10 of the drawings shows yet another embodiment of anchor plate 60having an opening 62 there through having irregular wall portions 64. Inthe embodiment of FIG. 10 the irregular wall portions 64 take the formof alternating peaks 66 and valleys 68 extending about the entire wallportion of the opening 62. While not specifically shown, it will beapparent that a mechanical interlock connection is made between theirregularly configured wall portions 64 of the anchor plate 60 in thesame manner as the embodiments of FIGS. 4 and 6. That is, a rebar havinga nominal diameter smaller than the opening 62 is first heated and theninserted into the opening 62 where it is forged, thereby upsizing theheated end of the rebar and filling all of the spaces around thealternating peaks 66 and valleys 68 to create a mechanical interlockbetween the rebar and the anchor plate 60.

While in the embodiment of FIG. 4 of the drawings, the anchor plate 32is shown as round, the anchor plate may take various otherconfigurations, including a polygonal shape and more specifically, arectangular shape as shown at 35 in FIG. 9 of the drawings or a squareshape as shown at 33 in FIG. 8 of the drawings. It will also be apparentthat the anchor plates 42 and 60 may also assume round, palegamal,rectangular and square shapes, similarly to the embodiment of FIG. 4 ofthe drawings.

Regardless of the specific configuration of the anchor plate it will beapparent that the present invention provides a method of fasteningsecurely an anchor plate to an standard rebar by forming an irregularlyshaped wall portion defining an opening through the anchor plate,heating an end of the rebar, inserting it into the opening in the anchorplate and then forging the heated end of the rebar to upsize it and fillthe interstices provided by the irregular wall portions of the openingthrough the anchor plate, resulting in a secure mechanical interlockbetween the end of the rebar and the anchor plate. Thus, the advantagesof utilizing an end anchor in place of merely bending the terminalportion of a rebar and inserting a crossing rebar are obtained, butwithout the expenditure of energy and expense associated with endanchors of this type. While the methods and structures formed therebydescribed herein constitute preferred embodiments of the invention it isto be understood that the invention is not limited to these preciseforms of method and structure formed thereby and that changes may bemade therein without departing from the scope of the invention asdefined in the appended claims.

1. A rebar end anchor comprising: an anchor plate, an opening formedthrough said anchor plate, said opening having irregular wall portions,a rebar having an anchor end and an outer surface and deformationsformed in said outer surface, said rebar anchor end being received insaid anchor plate opening and forged into mechanical interlock with saidirregular wall portions of said opening.
 2. The combination of claim 1wherein said rebar is of substantially constant diameter prior to beingforged into mechanical interlock with said irregular wall portions ofsaid opening through said anchor plate.
 3. The combination of claim 2wherein said rebar diameter is smaller than said opening through saidanchor plate.
 4. The combination of claim 3 wherein said irregular wallportions comprise circular grooves.
 5. The combination of claim 4wherein said grooves comprise threads.
 6. The combination of claim 3wherein said irregular wall portions comprise a counterbore formed insaid opening in said anchor plate.
 7. The combination of claim 3 whereinsaid irregular wall portion comprise alternating peaks and valleysprojecting inwardly in said opening.
 8. The combination of claim 1wherein said anchor plate is substantially round.
 9. The combination ofclaim 1 wherein said anchor plate is polygonal.
 10. The combination ofclaim 1 wherein said anchor plate is rectangular.
 11. A reinforcedconcrete structure comprising: a concrete body; a concrete beamintersecting said body, a reinforcing bar imbedded in said body and saidbeam and having an end terminating in said body, an end anchor plate, anopening formed through said anchor plate, said opening having irregularwall portions, and said end of said reinforcing bar being received insaid opening and forged into mechanical interlock with said irregularwall portions of said opening.
 12. The structure of claim 11 whereinsaid reinforcing bar is substantially constant in diameter prior tobeing forged into mechanical interlock with said irregular wall portionsof said opening through said anchor plate.
 13. The structure of claim 12wherein said reinforcing bar diameter is smaller than said openingthrough said anchor plate.
 14. The structure of claim 13 wherein saidirregular wall portions comprise circular grooves.
 15. The structure ofclaim 14 wherein said grooves comprise threads.
 16. The structure ofclaim 13 wherein said irregular wall portions comprise a counterboreformed in said opening through said anchor plate.
 17. The structure ofclaim 13 wherein said irregular wall portions comprise alternating peaksand valleys projecting into said opening in said anchor plate.
 18. Thestructure of claim 11 wherein said anchor plate is substantially round.19. The structure of claim 11 wherein said anchor plate is polygonal.20. The structure of claim 19 wherein said anchor plate is substantiallyrectangular.
 21. A method of manufacturing a rebar with end anchorcomprising: providing an anchor plate, forming an opening through saidanchor plate having irregular wall portions, providing a length of rebarhaving an anchor end, heating said anchor end of said rebar, insertingsaid heated anchor end of said rebar into said opening in said anchorplate, and forging said heated anchor end of said rebar into mechanicalinterlock with said irregular wall portions of said opening in saidanchor plate.
 22. The method of claim 21 wherein said rebar is ofsubstantially constant diameter prior to being forged into mechanicalinterlock with said irregular wall portions of said anchor plate. 23.The method of claim 22 wherein said substantially constantly diameter ofsaid rebar is smaller than said opening through said anchor plate. 24.The method of claim 23 wherein said irregular wall portions comprisecircular grooves.
 25. The method of claim 24 wherein said circulargrooves comprise threads.
 26. The method of claim 23 wherein saidirregular wall portions comprise a counterbore formed in said openingthrough said anchor plate.
 27. The method of claim 23 wherein saidirregular wall portions comprise alternating peaks and valleysprojecting into said opening in said anchor plate.
 28. The method ofclaim 21 wherein said anchor plate is substantially round.
 29. Themethod of claim 21 wherein said anchor plate is substantially polygonal.30. The method of claim 29 wherein said anchor plate is substantiallyrectangular.